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Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions.
Exp Physiol 2019; 104(3):345-358EP

Abstract

NEW FINDINGS

What is the central question of this study? Controlled-hyperthermia heat-acclimation protocols induce an array of thermoregulatory and cardiovascular adaptations that facilitate exercise in hot conditions. We investigated whether this ergogenic potential can be transferred to thermoneutral normoxic or hypoxic exercise conditions. What is the main finding and its importance? We showed that heat acclimation did not affect maximal cardiac output or maximal aerobic power in thermoneutral normoxic or hypoxic conditions. Heat acclimation augmented the sweating response in thermoneutral normoxic conditions. The cross-adaptation theory, according to which heat acclimation could facilitate hypoxic exercise capacity, is not supported by our data.

ABSTRACT

Heat acclimation (HA) mitigates heat-induced decrements in maximal aerobic power (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math>) and augments exercise thermoregulatory responses in the heat. Whether this beneficial effect of HA is observed in hypoxic or thermoneutral conditions remains unresolved. We explored the effects of HA on cardiorespiratory and thermoregulatory responses to exercise in normoxic, hypoxic and hot conditions. Twelve men [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> 54.7(standard deviation 5.7) ml kg-1 min-1 ] participated in a HA protocol consisting of 10 daily 90-min controlled-hyperthermia (target rectal temperature, Tre = 38.5°C) exercise sessions. Before and after HA, we determined <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> in thermoneutral normoxic (NOR), thermoneutral hypoxic (fractional inspired O2 = 13.5%; HYP) and hot (35°C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. Preceding each maximal cycling test, a 30-min steady-state exercise bout at 40% of the NOR peak power output was used to evaluate thermoregulatory responses. Heat acclimation induced the expected adaptations in HE: reduced Tre and submaximal heart rate, enhanced sweating response and expanded plasma volume. However, HA did not affect <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> or maximal cardiac output (P = 0.61). The peak power output was increased post-HA in NOR (P < 0.001) and HE (P < 0.001) by 41 ± 21 and 26 ± 22 W, respectively, but not in HYP (P = 0.14). Gross mechanical efficiency was higher (P = 0.004), whereas resting Tre and sweating thresholds were lower (P < 0.01) post-HA across environments. Nevertheless, the gain of the sweating response decreased (P = 0.05) in HYP. In conclusion, our data do not support a beneficial cross-over effect of HA on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> in normoxic or hypoxic conditions.

Authors+Show Affiliations

Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia. Jozef Stefan International Postgraduate School, Ljubljana, Slovenia.Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia. Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia.Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia.Department of Environmental Physiology, School of Chemistry, Biotechnology and Health, Royal Institute of Technology, Solna, Sweden.Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia. Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

30536521

Citation

Sotiridis, Alexandros, et al. "Heat Acclimation Does Not Affect Maximal Aerobic Power in Thermoneutral Normoxic or Hypoxic Conditions." Experimental Physiology, vol. 104, no. 3, 2019, pp. 345-358.
Sotiridis A, Debevec T, Ciuha U, et al. Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions. Exp Physiol. 2019;104(3):345-358.
Sotiridis, A., Debevec, T., Ciuha, U., Eiken, O., & Mekjavic, I. B. (2019). Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions. Experimental Physiology, 104(3), pp. 345-358. doi:10.1113/EP087268.
Sotiridis A, et al. Heat Acclimation Does Not Affect Maximal Aerobic Power in Thermoneutral Normoxic or Hypoxic Conditions. Exp Physiol. 2019;104(3):345-358. PubMed PMID: 30536521.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions. AU - Sotiridis,Alexandros, AU - Debevec,Tadej, AU - Ciuha,Urša, AU - Eiken,Ola, AU - Mekjavic,Igor B, Y1 - 2019/01/25/ PY - 2018/07/26/received PY - 2018/12/10/accepted PY - 2018/12/12/pubmed PY - 2019/8/27/medline PY - 2018/12/12/entrez KW - cardiac output KW - cross-adaptation KW - heat training SP - 345 EP - 358 JF - Experimental physiology JO - Exp. Physiol. VL - 104 IS - 3 N2 - NEW FINDINGS: What is the central question of this study? Controlled-hyperthermia heat-acclimation protocols induce an array of thermoregulatory and cardiovascular adaptations that facilitate exercise in hot conditions. We investigated whether this ergogenic potential can be transferred to thermoneutral normoxic or hypoxic exercise conditions. What is the main finding and its importance? We showed that heat acclimation did not affect maximal cardiac output or maximal aerobic power in thermoneutral normoxic or hypoxic conditions. Heat acclimation augmented the sweating response in thermoneutral normoxic conditions. The cross-adaptation theory, according to which heat acclimation could facilitate hypoxic exercise capacity, is not supported by our data. ABSTRACT: Heat acclimation (HA) mitigates heat-induced decrements in maximal aerobic power (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math>) and augments exercise thermoregulatory responses in the heat. Whether this beneficial effect of HA is observed in hypoxic or thermoneutral conditions remains unresolved. We explored the effects of HA on cardiorespiratory and thermoregulatory responses to exercise in normoxic, hypoxic and hot conditions. Twelve men [ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> 54.7(standard deviation 5.7) ml kg-1 min-1 ] participated in a HA protocol consisting of 10 daily 90-min controlled-hyperthermia (target rectal temperature, Tre = 38.5°C) exercise sessions. Before and after HA, we determined <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> in thermoneutral normoxic (NOR), thermoneutral hypoxic (fractional inspired O2 = 13.5%; HYP) and hot (35°C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. Preceding each maximal cycling test, a 30-min steady-state exercise bout at 40% of the NOR peak power output was used to evaluate thermoregulatory responses. Heat acclimation induced the expected adaptations in HE: reduced Tre and submaximal heart rate, enhanced sweating response and expanded plasma volume. However, HA did not affect <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> or maximal cardiac output (P = 0.61). The peak power output was increased post-HA in NOR (P < 0.001) and HE (P < 0.001) by 41 ± 21 and 26 ± 22 W, respectively, but not in HYP (P = 0.14). Gross mechanical efficiency was higher (P = 0.004), whereas resting Tre and sweating thresholds were lower (P < 0.01) post-HA across environments. Nevertheless, the gain of the sweating response decreased (P = 0.05) in HYP. In conclusion, our data do not support a beneficial cross-over effect of HA on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>peak</mml:mi> </mml:mrow> </mml:msub> </mml:math> in normoxic or hypoxic conditions. SN - 1469-445X UR - https://www.unboundmedicine.com/medline/citation/30536521/Heat_acclimation_does_not_affect_maximal_aerobic_power_in_thermoneutral_normoxic_or_hypoxic_conditions_ L2 - https://doi.org/10.1113/EP087268 DB - PRIME DP - Unbound Medicine ER -